Figure 6: Histological findings of the subscapularis tendons in group 1 (SAL), group 2 (PDRN), group 3 (MSC), and group 4 (MSC + PDRN). (A1–A4) Newly regenerated tendons are shown in the blue-stained fibers (black arrow; Masson’s trichrome stain; X200) in groups 2, 3, and 4. Few regenerative collagen fibers were seen in group 1. (B1–B4) Regenerated tendon fibers (black arrow; X200) were stained with anti-type 1 collagen antibody in groups 2, 3, and 4. Few regenerated tendon fibers were seen in group 1. (C1–D4) Numerous BrdU- and PCNA-stained cells (black arrow, X400, X200) were observed in regenerated tendon fibers in groups 2, 3, and 4. Few BrdU- and PCNA-stained cells were observed in group 1. (E1-F4) Numerous VEGF-positive cells and PECAM-1 positive microvascular densities (black arrows, X200) were observed in groups 2, 3, and 4. Few VEGF-positive cells and PECAM-1-positive microvascular densities were observed in group 1. MTS: Masson’s trichrome stain; COL-1: collagen type 1; BrdU: 5-bromo-2-deoxyuridine; PCNA: proliferating cell nuclear antigen; MSC: human umbilical cord blood-derived mesenchymal stem cell; PDRN: polydeoxyribonucleotide; VEGF: vascular endothelial growth factor; PECAM: platelet endothelial cell adhesion molecule.